Atomic layer deposition (ALD) involves the deposition of successive monolayers over a substrate within a deposition chamber typically maintained at subatmospheric pressure. An exemplary such method includes feeding a single vaporized precursor to a deposition chamber effective to form a first monolayer over a substrate received therein. Thereafter, the flow of the first deposition precursor is ceased and an inert purge gas is flowed through the chamber effective to remove any remaining first precursor which is not adhering to the substrate from the chamber. Subsequently, a second vapor precursor different from the first is flowed to the chamber effective to form a second monolayer on/with the first monolayer. The second monolayer might react with the first monolayer. Additional precursors can form successive monolayers, or the above process can be repeated until a desired thickness and composition layer has been formed over the substrate.
It is a desired intent or effect of the purging to remove gas molecules that have not adsorbed to the substrate or unreacted gas or reaction by-products from the chamber to provide a clean reactive surface on the substrate for the subsequent precursor. In the context of this document, a reaction by-product is any substance (whether gas, liquid, solid or mixture thereof) which results from reaction of any deposition precursor flowing to the chamber and that is not desired to be deposited on the substrate. Further in the context of this document, an intermediate reaction by-product or reaction intermediate by-product is a reaction by-product formed by less than complete reaction of a precursor to form a desired monolayer on the substrate. Where there is a great degree of varying topography and/or there are high aspect ratio features on the substrate, it can be difficult to move the unreacted gases or reaction by-products from deep within openings for ultimate removal from the chamber. Further, certain reaction by-products, particularly intermediate reaction by-products, may not be gaseous and may not completely react to form gaseous reaction by-products in the typical short precursor pulse times. Accordingly, the purge gas pulse may not be effective or sufficient in removing such intermediate reaction by-products from the substrate and chamber.
For example, consider that in an atomic layer deposition of titanium nitride using TiCl4 and NH3, the desired deposition product is TiN with HCl gas being the desired principle gaseous by-product. Consider also that there might be reaction intermediate by-products which might, even if gaseous, be difficult to remove from substrate openings. Further, if certain reaction intermediate by-products are solid and/or liquid phase prior to HCl formation, complete removal can be even more problematic where less than complete reaction to TiN and HCl occurs.
Consider also the atomic layer deposition of Al2O3 using trimethylaluminum (TMA) and ozone as alternating deposition precursors. Apparently in such deposition, achieving an effective ozone precursor feed can be somewhat of a challenge due to the limited lifetime of ozone within the chamber. Specifically, an ozone molecule is in an inherently unstable, reactive form of oxygen which can rapidly dissociate and/or combine with another ozone molecule to form three O2 molecules. Regardless, a desired goal in the ozone feed is adsorption of oxygen atoms from the O3 to the surface of the substrate with O2 as the reaction by-product which is driven off. Of course, the O2 which forms deep within openings on the substrate has to be removed therefrom while more O3 needs to get into the openings to form a complete monolayer of oxygen atoms adhering to the substrate. In other words, the O2 which forms is trying to get out while more O3 is trying to get in.
While the invention was motivated in addressing the above issues and improving upon the above-described drawbacks, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded (without interpretative or other limiting reference to the above background art description, remaining portions of the specification or the drawings) and in accordance with the doctrine of equivalents.